"I fill up at least once a week, so that's at least $20 a month. That's a lot of money," Barbusca said. "Of course, I can't do a lot about it. I guess I could picket, but it's a little too cold for that."

The wintertime price increase is not the norm in the fuel business, where low consumer demand and high supply tend to make gasoline cheapest in January. But factors outside the U.S. have pushed prices higher in the past month, and some believe they're likely to continue rising.

"We're seeing more issues weigh on oil prices (such as Venezuela's low oil production and high Chinese demand) that have been creating somewhat of a storm at the pump," said Patrick DeHaan, senior fuel analyst at GasBuddy.com.

He expects gas prices to rise by another 40 cents a gallon in the early spring, and predicted the return of $3-a-gallon unleaded fuel in many areas of the country by mid-summer.

"Once refinery maintenance season begins en masse by mid-March, gasoline production ability will be diminished, sending prices higher," DeHaan said, referring to the annual spring practice of temporarily closing each refinery to switch to an EPA-mandated summer blend of fuel.

"To make things worse yet, the transition to summer gasoline will constrain supply further and eventually send prices up at a faster pace than what we're currently seeing," DeHaan said.

Meanwhile, world supply of crude oil has been reduced by the collapse of the economy in oil-rich Venezuela, and by the 2017 decision by OPEC countries to cut production, pushing the price of crude oil to $66.05 a barrel Friday morning. That was the highest level since December 2014.

It's also more than double the price of oil one year ago, when it stood at $29.88 per barrel. The increase of $36 per barrel in the past year is significant, because oil prices determine two-thirds of the price of gasoline and diesel.

The collapse of Venezuela's economy and an oil production cut by OPEC have helped push fuel prices higher in the United States.(Photo: Ken Ruinard/Independent Mail)

The average price of unleaded fuel has climbed about 5 cents per gallon in the past week, and is up 13 cents a gallon in the past month.

Friday's average price of diesel fuel, which is used by most commercial transporters, stood at $2.49 per gallon in Anderson and Greenville counties.

The steady price increase of recent weeks comes at a time when U.S. oil production has reached a milestone — 10 million barrels of oil per day, the highest level since 1970 and very close to an all-time record.

But U.S. oil exports, legalized two years ago, have drained supply from the U.S.

Gas prices could reach $3 a gallon in many parts of the country by mid-summer, according to experts.(Photo: Ken Ruinard/Independent Mail)

U.S. oil inventories are down 77 million barrels from one year ago, "a tremendous drop," DeHaan said.

GasBuddy.com tracks fuel prices on a real-time basis at about 140,000 fuel outlets across North America.